The present invention relates to the field of thermoset glass fibre reinforced composite laminates, particularly for use as high voltage insulation materials. Such thermoset sheets are usually manufactured by exposing a prepreg sheet to a pressing step in which the prepreg sheet is formed to a desired shape and is cured under elevated pressure and temperature.
It is common prepreg technology to use thickening agents to obtain a prepreg material that can be handled for loading in moulds. Isocyanates react fast with hydroxyl groups, and are therefore often used as thickening agents together with hydroxyl containing polymers or together with polyols, to obtain a fast thickening cycle. The prepreg is manufactured by preparing a composition containing hydroxyl containing polymers and isocyanate, and incorporating glass fibre reinforcing material. A problem that may arise in connection with the manufacture of composite laminate is that inferior mould flow properties in the resin blend may cause defects such as voids and fibre misalignment in the prepreg during pressing. Moreover, hitherto known prepregs need to undergo a maturation that may last for several days, also when elevated temperatures are used, before they can be exposed to the pressing treatment.
There is a need for a prepreg composition that has improved mould flow properties and that allows a more efficient production of prepregs for the manufacture of thermoset glass fibre reinforced composite laminates.